1. Field of the Invention
The present invention relates to an optical information recording and reproducing apparatus for performing an optical recording or optomagnetic recording with high density and large capacity, in particular, an optical information recording and reproducing apparatus for optically recording the information or optomagnetically recording the information with high density and large capacity such as the optical information recording and reproducing apparatus which is preferable for recording and reproducing the optical information with high density and high precision by use of the adjacent-field light (evanescent light), and for radiating the light from the tip end of the probe onto the optical information recording medium, and the optical information recording and reproducing apparatus applying the probe microscope.
2. Discussion of the Background
An optical information recording and reproducing apparatus for recording and reproducing the information with high density by use of the adjacent field light (evanescent light) has been already proposed.
For instance, in the published specification of Japanese Laid open Patent Publication No.7-192,280 (called xe2x80x9cBackground Art 1), a structure of the optical information recording and reproducing apparatus is proposed in FIG. 14 as the structure capable of raising the accuracy of the tracking control and enabling to use a disc-state recording medium in the high-density recording/reproducing operation utilizing the above-mentioned evanescent light.
In such structure, a laser light radiated (emitted) from the semiconductor laser (laser diode) 1 is focused by a lens 6, and the focused laser light is applied to an optical fiber 7 through an opening 8 thereof. A scanning head 9 formed on the tip end portion of the optical fiber 7 becoming thinner toward the tip end has an opening 10 of a diameter almost equal to or smaller than the wavelength of the laser light on the projecting end surface. A recording surface 11 moves relating to the opening 10. A reflection light taken out from the recording surface 11 through the scanning head 9 is detected by a light detector 13. A scanning control head 20 unitarily mounted in parallel with the scanning head 9 includes a semiconductor laser (laser diode) 15 employed as a peculiar (original) light source, a lens system, and optoelectric conversion element 19, and generates a tracking error detecting signal for positioning the scanning head 9 onto the track of the recording surface 7. An actuator 21 is controlled on the basis of the tracking error signal and thereby the tracking accuracy can be improved.
Background Art 2 (for the First-group Invention)
On the other hand, in the published specification of, Japanese Laid-open Patent Publication No.8-321,084 (called xe2x80x9cBackground Art 2xe2x80x9d), a structure of the optical information recording and reproducing apparatus is proposed in FIG. 15 as the structure capable of performing the positional control in the track width direction with high precision and performing the operation of recording/reproducing with high accuracy in the scanning type probe memory technology. In
In such structure, tracking probes 51 and 56 are provided adjacently to probes 52 through 55 in order to record and reproduce the information on a recording area 64. The positional control in the track width direction of the probes 52 through 55 for use in recording or reproducing is performed by a probe actuator 65 on the basis of the tracking error signal detected by the tracking probes 51 and 56, and thereby the positional control in the track width direction can be performed with high accuracy.
In the above-mentioned background arts 1 and 2, since the information is written in on the recording medium by use of the adjacent field light, the size of the recorded mark becomes almost several tens n m in the diameter thereof. Consequently, it is necessary to set the accuracy of the tracking for precisely writing in and reading out the recorded mark suitably to an extent of several nm.
However, although the above background arts 1 and 2 describe the detection medium for detecting the tracking error signal, those arts do not describe any concrete structure for finely moving (actuating) the probe in order to compensate the tracking error.
Background Art 3 (for the Second-group Invention)
The background art 3 described in the published specification of Japanese Laid-open Patent Publication No.7-192,280 raises the accuracy of the tracking control in the high-density recording/reproducing by use of the evanescent light, and enables to use the disc-state recording medium.
For this reason, as shown in FIG. 17, a laser light radiated (emitted) from the semiconductor laser (laser diode) 201 is focused by a lens 202, and the focused laser light is applied to an optical fiber 203 through an opening 204 thereof. A scanning head 205 formed on the tip end portion of the optical fiber 203 becoming thinner toward the tip end has an opening 206 of a diameter almost equal to or smaller than the wavelength of the laser light on the projecting end surface. A recording surface 207 of the recording medium moves relatively to the opening 206. A reflection light taken out from the recording surface 207 through the scanning head 205 is detected by a light detector 208. A scanning control head 209 unitarily mounted in parallel with the scanning head 205 includes a semiconductor laser (laser diode) 210 employed as a peculiar (original) light source, a lens system, and optoelectric conversion element 217, and generates a tracking error detecting signal for positioning the scanning head 205 onto the track of the recording surface 207.
The background art 4 described in the published specification of Japanese Patent Publication No, 8-321,084 performs the positional control in the track width direction with high accuracy in the scanning type probe memory technology and thereby performs the operation of recording or reproducing with high accuracy.
For this reason, as shown in FIG. 18, tracking probes 215 and 216 are provided adjacently to probes 211 through 214 for use in recording or reproducing the optical information. The positional control of the probes 211 through 214 for use in recording/reproducing in the track width direction is performed by the tracking error signal detected by the tracking probes 215 and 216.
Background Art 5 (for the second-group Incention)
The background art 5 described in the published specification of Japanese Patent Publication NO. 8-7323 provides an ultrahigh-density and small-size optical information recording and reproducing apparatus.
For this reason, as shown in FIG. 19, a semiconductor laser (laser diode) 221, a light detector 222, and an evanescent light generating probe 223 are respectively carried on a floating (surfacing) slider 224. The information is recorded on the recording medium 226 by the action of the evanescent light 225. When the information is reproduced, the electric current value of the semiconductor laser is biased with the threshold value, and as the result the S/N ratio can be improved.
The operation of tracking is performed in such way as mentioned below. Namely, as shown in FIG. 20 (FIGS. 20A and 20B), by use of the probe shown in FIG. 19, the evanescent light is formed in the track direction (the circular circumferential direction of the medium 226), and the light beam having a little (somewhat) spreading-out width is formed in the direction perpendicular to the track direction. It is preferable that the ratio of those two light beams diameters is 5:1. There exist a servo area 228 having previously formed prepit 227 and the data area 229. The prepit 227 is a wobble pit having a center respectively disposed on a place displaced right and left by a constant when the surface of the wobble pit is scanned by the light beam, if the light 30 deviates from the track center, there occurs an unbalanced state in the signal from the successive two prepits. Here, taking the difference between those signals the difference value is employed as the tracking error signal.
Background Art 6 (for the Second-group Invention)
The background art 6 described in the published specification of Japanese Laid-open Patent Application NO. 9-17047 performs the operation of accessing by the head with high speed and the control of positioning the head, and thereby attain a high-speed recording/reproducing.
For this reason, the operation of recording/reproducing is performed by use of the head constructed by combining a scanning type probe head for the recording/reproducing and an optical head for performing the positional control into one. Namely, in order to raise the speed of recording/reproducing, the light is used as the control signal in order to control the height and position of the recording/reproducing head. Namely, the background art 6 uses a complex type head having the scanning type probe head for recording/reproducing provided with the position controlling optical head.
In such complex type head, the scanning type probe head performs the recordinq/reproducing, while the optical head provided in the scanning type probe head performs the positional control for the probe head.
By utilizing the above-mentioned optical head, the control of positioning the probe head with high accuracy and the operation of recording/reproducing can be done with high speed. The mark on the plural tracks is recorded on the land portion of the recording medium, and the tracking operation is done by use of the head specially used for the tracking on the adjacent land portions also specially used for the tracking.
Background Art 7 (for the Second-group Invention)
The background art 7 described in the published specification of Japanese Laid-open Patent Publication No. 7-225,975 realizes the probe scanning with practically sufficient speed in the information recording and reproducing apparatus for scanning the probe along the surface of the recording medium and thereby performing the operation of recording/reproducing.
For this reason, as shown in FIG. 21, a linearly-polarized light flux emitted from the light source 231 passes through a polarization surface preserving type optical fiber 232 and forms an evanescent wave through a metal mask 234 having a fine opening portion 233 smaller than the wavelength of the above-mentioned light.
Here, since both of the metal mask 234 and an optomagnetic recording medium 236 are made of electrically conductive substance, electrodes are respectively attached to both of them and the electrodes are connected to a capacitance-distance sensor 235 and thereby the distance d can be detected from the capacitance value between both of the electrodes. As the effect thereof, since the square measure of the part opposing to the optomagnetic recording medium 236 of the metal mask 234 is larger than that of the opening portion 233, the information of the distance d can be obtained with high accuracy and high hand (width). The information of the distance d is fed back to the actuator 237 and the position of the fine opening portion 233 is controlled. Thereby, a high-speed probe scanning can be done.
Background Art 8 (for the Second-group Invention)
The background art 8 described in the published specification of Japanese Laid-open Patent Publication No. 7-21564 can always accurately control the distance between the probe and the recording layer in every operational situation of the Foton STM type optical memory.
For this reason, as shown in FIG. 22, the first light 242 is guided in a transparent body 241 having a fine opening portion at the tip end thereof. A recording layer 244 of the light; recording medium 245 is mounted in the first evanescent field 243 formed at the fine opening portion. The information is recorded in the light recording medium 245 by use of the first light 242 or the recorded information is reproduced.
On the other hand, the second light 246 having a different wavelength from that of the first light 242 is guided in the light recording medium 245. The light thus guided detects the second evanescent wave 247 formed on the surface of the light recording medium by (through) the transparent body 241. The detected light is separated from the guided light due to the first light 242 by use of a wavelength separating medium 248, and the intensity of the second light 246. Thereby, the distance between the transparent body 41 and the light recording medium 245 can be adjusted.
Background Art 9 (for the Second-group Invention)
In the background art 9 described in the published specification of Japanese Laid -open Patent Publication No. 10-172,172 in the information recording and reproducing apparatus applying the probe microscope, when there exists the manufacturing error or the time-elapsing variation in the shape of the optical probe, the distance between the optical probe and the recording medium cannot be kept constant and it is difficult to abstain a predetermined recording density. In consideration of such problems, even though there exists a reason of the optical probe resolution varying occurrence such as the unevenness of the probe shape, the time-elapsing variation, the predetermined recording density can be kept (maintained).
For this reason, as shown in FIG. 23, periodical patterns 250 and 251 respectively having different periods are provided on the recording medium 249, and those periodical patterns 250 and 251 are detected by an optical probe 252. The frequencies of the obtained signals are analyzed and compared with each other. In such way, the distance between the optical probe 252 and the recording medium 249 is detected. When the distance H is large, the component of the high spatial frequency becomes small, and the distance H can be measured by the above component of the high spatial frequency.
Background Art 10 (for the third-group Incention)
Conventionally, as the information recording and reproducing apparatus, there exists the apparatus intending to realize a high-density information recording and reproducing apparatus by utilizing the probe microscope. On this occasion, when there exists the manufacturing error or the time-elapsing variation in the optical probe shape, the distance between the optical probe and the recording medium cannot be kept constant, and thereby it is difficult to obtain the predetermined recording density.
Here, for instance, the background art 10 described in the published specification of Japanese Laid-open Patent Publication No. 10-172172 proposes a high-density information recording and reproducing apparatus which can keep the predetermined recording density even though there exists a reason of varying the resolution of the optical probe such as the unevenness or the time-elapsing variation in the shape of the optical probe.
According to the background art 10, as shown in FIG. 55, periodical patterns 402 and 403 respectively having different periods xcex91 and xcex92 are provided on the recording medium 401. Those periodical patterns 402 and 403 are detected by an optical probe 404, and the frequency of the signal thus obtained is analyzed and compared with each other. In such way, the distance H between the optical probe 404 and the recording medium 401 can be detected. The reference numeral 405 represents a semiconductor laser (laser diode), and the numeral 406 represents a lens. The optical probe 404 is formed by a projecting portion 407b at the tip end of an optical fiber 407 having a core 407a and covered with a metal film 408. The reference numeral 409 represents an optical detector.
According to such structure, the magnitude of the fundamental wave component I of the light amount (intensity) variation at the time of scanning the periodical patterns 402 and 403 with the optical probe 403 becomes xe2x80x9cH: smallxe2x80x9d as shown in FIG. 56 when the distance H between the recording medium 401 and the optical probe 404 is small. On the contrary, when the distance H is large, the magnitude of the fundamental wave component I becomes xe2x80x9cH: largexe2x80x9d.
Namely, when the distance H is large, the component of the high spatial frequency K becomes small. In such situation, by scanning those periodical patterns 402 and 403 and taking the difference of the fundamental component of the light intensity variation, the distance H between the optical probe 404 and the periodical patterns 402 and 403 (namely, recording medium 401).
Here, the spatial frequencies K1 and K2 of the periodical patterns 402 and 403 can be respectively obtained by the following equations:
K1=2xcfx80/xcex91, and
K2=2xcfx80/xcex92.
Background Art 11 (for the Third-group Invention)
Furthermore, there has been proposed an information recording and reproducing apparatus employing an optical fiber emitting the light from the tip end thereof as the probe, in the background art 11. Referring to FIGS. 57 through 59, the background art 11 is described hereinafter.
At first, the optical fiber emitting the light from the tip end thereof is employed as the probe 411 and put on a slider 412 as shown in FIG. 57. For instance, it may be allowable that the flying slider not brought into contact with the recording medium 415 composed of a base board 413, a recording layer, and a protection layer 14, etc. or the contact slider brought into contact with the same is used as the slider 412. Here, a spindle motor for rotating the recording medium 415 is fixed on the same baseboard through a suspension 416, an arm 417, and an arm motor not shown. In such structure, the slider 12 is movably mounted so as to be moved in the tracking direction of the recording medium 415 by the arm motor for rotating the recording medium 415. However, the slider 412 can be moved in the tracking direction of the recording medium 15 by the arm motor. By the action of those sliders 12, the distance between the recording medium 415 and the tip end of the probe 411 can be stably kept to several tens nm during the period of the recording medium 415 rotation.
As shown in FIG. 58, mark pits 418 are arranged in the circumferential direction (track direction) on the surface of recording medium 415 or in the vicinity of the surface thereof, and the information is written in. Since the recording medium 415 rotates, unless the tracking of the probe 411 is performed so as to put the tip end of the probe 411 on the center line of the mark pit 418, it is impossible to write in or read out the correct information.
FIG. 59 is an enlarged cross-sectional structural view showing the vicinity of the probe 411 shown in FIG. 57 which is cut in the radius direction. The probe 411 of the optical fiber structure includes a core 419a and a clad 419b. The upper-edge base (root) side of the probe 411 is fixed on the slider 412 through a common electrode portion 20, while the tip end side 411a of the probe 411 opposing to the recording medium 415 is put in a free state. The probe 411 has a so-called cantilever (arm) structure. The tip end 411a thereof is made finely sharpened utilizing the method of etching. A light intercepting metal film 421 entirely covers the circumference of the probe 411 such that the light is emitted only through the small opening of the tip end 411a. The diameter of the opening is equal to or smaller than the wavelength of the light propagating (transmitted) through the optical fiber. The so-called adjacent field light (called xe2x80x9cevanescent lightxe2x80x9d) is emitted from the above opening.
Furthermore, in the background art 11, since it is allowed to use the probe having the cantilever structure, the probe is not limited, in particular, to the adjacent field light. It may be also allowed to use the probe having an opening diameter larger than the employed wavelength, for instance, the internal-concentration type probe. The writing-in and reading-out operations of the information for the recording medium are performed by use of the light. The light-intercepting metal film 421 covering the probe 411 is grounded (connected to the earth).
Furthermore, a pair of electrodes 422 and 423 are provided so as to nip the probe 411 in the radius direction of the recording medium 415 (tracking direction) at the time of using the slider 412. Those electrodes 422 and 423 are fixed in the slider 412. Different voltages V1 and V2 are respectively applied across the electrodes 422 and 423 and the common electrode 420 of the probe 11 (light-intercepting metal film 421). Thereby, an electrostatic attractive farce occurs between the electrodes 424 and 425 and the probe 411 is in a state of a cantilever, and the tip end 411a thereof swings in the radius direction of the recording medium 415. Thereby, the movement (actuation) of the tip end 411a of the probe 411 necessary for the tracking is done.
In FIG. 59, when the tip end 411a of the probe 411 is moved in the direction {circle around (1)}, only the voltage V1 is applied to the electrode 22 and-the voltage V2 is not applied to the electrode 23. When the tip end 411a of the probe 411 is moved in the direction {circle around (2)}, vice versa. Namely, only the voltage V2 is applied to the electrode 23 and the voltage V1 is not applied to the electrode 22. On this occasion, the electrostatic attractive farce F1 in the direction {circle around (1)} is expressed by the below equation (1), while the electrostatic attractive force F2 in the direction {circle around (2)} is expressed by the below other equation (2).
xe2x80x83F1=xe2x88x92(xc2xd)(∂C1/∂d1)V12xe2x88x92(xc2xd)(V12/d12)xcex5aS1xe2x80x83xe2x80x83(1)
F2=xe2x88x92(xc2xd) (∂C2/∂d2)V22xe2x88x92(xc2xd) (V22/d22)xcex5aS2xe2x80x83xe2x80x83(2)
In the above equations (1) and (2), c1 and c2 represent respective electrostatic capacitances between the probe 411 and the electrodes 422, 423, S1 and S2 equivalent square measures of the electrostatic capacitances c1, c2, d1 and d2 respective distances between the probe 411 and the electrodes 22, 23, and xcex5a permittivity (dielectric rate) of the air. Furthermore, the electrostatic, capacitances c1 and c2 are assumed to be expressed by the following equations (3) and (4):
C1=xcex5axc2x7S1/d1xe2x80x83xe2x80x83(3)
C2=xcex5axc2x7S2/d2xe2x80x83xe2x80x83(4)
Consequently, the electrostatic attractive force is proportional to the square (value) of the voltage and inversely proportional to the square (value) of the distance.
As the method of applying the voltage for moving the tip end 411a of the probe 411, in addition to the above-mentioned method of applying the voltage only to the electrode in the desired direction of moving the probe 411, there exists another method of superposing the bias voltage V6 and the control voltage xcex94V and simultaneously applying the voltage thus superposed to both of the electrodes 22 and 23.
Namely, the voltages V1 and V2 as expressed by the below equations are applied to the electrodes.
V1=Vb+xcex94Vxe2x80x83xe2x80x83(5)
V2=Vbxe2x88x92xcex94Vxe2x80x83xe2x80x83(6)
By changing the control voltage xcex94V, the tip end 411a of the probe 411 is moved.
Consequently, the force F exerted onto the probe 411 is expressed by the below equation (7).
F=F1=F2=xc2xd(V12/d12)xcex5aS1xe2x88x92xc2xd(V22/d22)xcex5aS2=[(2xcex94V+V)/d2]xcex5aSxe2x80x83xe2x80x83(7)
Here, the following equations are assumed:
S1=S2xe2x80x83xe2x80x83(8)
d1≈d2=dxe2x80x83xe2x80x83(9)
Under such assumption, since the electrostatic attractive force is proportional to the control voltage xcex94V, the control operation therefor can be facilitated.
Background Art 12 (for the Third-group Invention)
As the background art 12, there exists an example of the proposal as shown in FIG. 60. Firstly, a laser light source 431 continuously oscillates (CW) and the light emitted therefrom is focused onto the end surface of the optical fiber 433 by the action of a coupling lens 432 and enters the core of the optical fiber 433. The light thus focused and entering the core exists as the adjacent field light at the place very near (several tens nm) to the sharpened tip end of the optical fiber 433.
Furthermore, in the background art 12, since it is allowed to use the probe having the cantilever structure, the probe is not limited, in particular, to the probe emitting the adjacent field light. Namely, the probe paving the opening diameter larger than the employed wavelength, for instance, an internal light-focusing type probe can be used.
Consequently, the light existing in the vicinity of the tip end of the optical fiber is not limited, in particular, to only the adjacent field light. Namely, the propagating light emitted from the tip end of the internal light-focusing type probe, or the light mixedly including the propagation light and the adjacent field light can be also allowed to be used.
A recording medium 434 is rotated by a spindle motor 435. An information is recorded on the surface of the recording Medium 34 by an area (mark) having a contrast of the transmission sate (factor). When the tip end of the optical fiber 433 functioning as a probe 436 is put onto a position several tens nm or less from the-surface of the recording medium 434, the adjacent field light spreading out from the tip end of the probe 436 propagates to the recording medium, and the transmission light having the power corresponding to the transmission factor of the aforementioned mark comes out at the opposite side to that of the probe 436 of the recording medium 437. The light enters a photomultiplier (PMT) 438 through a coupling lens 437. The PMT 438 converts the entering light to an electric signal. The signal thus converted is amplified by a pre-amplifier 439, and thereafter the amplified signal is converted to a digital signal by a binarizing circuit 440, and the converted signal is inpuktted into the computer 441, and then the information on the recording medium 434 is read out in the computer 441. Since the recording medium 434 and the probe 436 move relatively to each other, the information recorded on the marks arranged in the circular circumferential direction (track direction) is stored in the computer 441, in order of a time series.
Even in the other similar apparatus capable of writing in the information into the recording medium 434, the data can be written in the information in the similar way. The necessary writing-in pulse is applied to an LD driver 442 by the computer 441, and the signal thus applied thereto drives the laser light source 431. In such way, the information is written in order on the surface of the recording medium 434.
On this occasion, it is necessary to set the distance between the surface of the recording medium 434 and the tip end of the probe 436 to several tens nm. In practice, the recording medium 434 has convex and concave surface. In addition, usually, the recording medium 434 itself causes surface movement when it rotates, and the same 434 move up and down. Therefore, it is necessary to control the distance therebetween so as to make it constant. In order to perform such control, the shear force or the electrostatic attractive force based on the force between atoms is utilized for the surface of the recording medium 434 and the tip end of the probe 436.
Here, the probe 436 is bonded, with adhesive agent, on the one-side cantilever of a crystallized quartz (crystal) vibrator 443. The crystallized quartz vibrator 443 is connected to a piling-layer type piezoelectric element 445 through an L-shaped holder 444. The piling-layer type piezoelectric element 445 is connected onto a sliding-proof pad 446. The sliding-proof pad 446 is brought into contact with the surface of the recording medium 434. When the recording medium 434 rotates, the sliding-proof pad 446 slidably moves on the recording medium 434. As the result, there occurs a relative movement between the recording medium 434 and the probe 436. When the voltage is applied to the piling-layer type piezoelectric element 445, the element 445 is expanded and contracted in the Z-direction. Therefore, the distance between the probe 436 and the surface of the recording medium 434 can be changed.
The crystal vibrator 443 is vibrated by the crystallized quartz element 447, and thereby the resonance frequency can be changed. When the surface of the recording medium 434 approaches the tip end of the probe 436, the shear force or the electrostatic attractive force based on the force between the atoms is exerted between the surface of the recording medium 434 and the tip end of the probe 436. The above force acts as the spring existing between the surface of the recording medium 434 and the tip end of the probe 436. In such structure, the resonance frequency of the entire vibration system can be changed. However, since the frequency of vibrating by the piezoelectric element 447 does not change at all compared with that at the former time, the state of the entire vibration system is put outside of the resonant state, and thereby the amplitude of the vibration is reduced.
The voltage created by the crystallized quartz vibrator 443 is amplitude by the differential amplifier 448, and the voltage thus amplified is inputted into a lock-in amplifier 449. The lock-in amplifier 449 amplifies the amplitude signal of the crystallized quartz vibrator and converts the amplified signal to DC voltage in synchronism with the vibration frequency. The out-put of the lock-in amplifier 449 is converted from analog signal to digital signal by an analog-to-digital (A/D) converter 451, and the digital signal thus converted is taken into the computer 441.
From the difference of the desired distance between the probe 436 and the surface of the recording medium 434 from the standard value corresponding thereto, the computer 441 computes the numerical value for controlling the distance between the probe 336 and the surface of the recording medium 434 and outputs the computed numerical value therefrom. The output voltage outputted from the computer is converted to an analog voltage by a digital-to-analog (D/A) converter 452. Thereafter, the analog signal thus converted is amplified by a power amplifier 453 and inputted into the piling-layer type piezoelectric element 445. In such way, the distance between the probe 436 and the surface of the recording medium 434 is controlled by the computer 441.
Here, the entire objects carried on the sliding mechanism including the sliding-proof pad 446 is called a xe2x80x9csliderxe2x80x9d, hereinafter. The slider 454 is fixed on the base board on which a spindle motor 435 is fixed through the suspension, the arm, and the arm motor, all not shown in the drawing (FIG, 60). Refer to the structure shown in FIG. 57.
However, the slider 454 can move in the tracking direction by the action of the arm motor and further move up and down in the z direction by the suspension. On the other hand, the slider 454 is pressed against the surface of the recording medium 434 with suitable force by the suspension, and the sliding-proof pad 446 is brought into contact with the surface of the recording medium 434.
When the information recording and reproducing apparatus as mentioned heretofore is put in a waiting state, the probe 436 is separated at a long distance from the recording medium 434 so as not to bring the probe 436 into contact with the recording medium 434. Therefore, as mentioned above, before starting the operations of writing-in or reading-out, it is necessary to perform the works of bringing the probe 436 to the place near the surface of the recording medium 434.
On this occasion, as mentioned above, if the distance between the probe 436 and the recording medium 434 is intended to know only by the shear force, the approach of the probe 436 to the surface of the recording medium 434 cannot be known until the distance therebetween approaches to several tens nm. Thereby, a collision is apt to happen therebetween.
In such situation, according to the proposal of the background art 12, such problems can be solved by causing an electric be solved by causing an electric potential difference between the probe 436 and the surface of the recording medium 434.
As the premise (precondition) thereof, it is necessary that the probe 436 needs to be made of electrically conductive substance from the bottom to the tip end thereof and the recording medium 434 also need to be conductive. Regarding the probe 436 utilizing the optical fiber 433 to be employed for the measurement of the adjacent field light, since the emission of the light from the clad causes noise, the clad is treated with metal in order to avoid such noise. Therefore, the former condition is satisfied generally.
Furthermore, the recording medium 434 made of optomagnetic material, phase-variation material, etc. is conductor or semiconductor, and therefore the resistivity (specific resistance) thereof is low. Consequently, on many occasions, the recording medium 434 also satisfies the latter condition.
Under such precondition, a switch 455 capable of being changed over and controlled by the computer 441 is further provided in the apparatus. At first, a power source 456 of voltage Va is connected to light-intercepting metal film of the probe 436 by the switch 455. Since the metal film can be attached to the entire portion of the optical fiber 433, the power source 456 is connected to the bottom (base) portion of the optical fiber 433 (probe 436) and thereby the voltage Va 
Can be applied to the tip end of the probe 436. The recording medium 434 is connected to the standard electric potential (ground) through the shaft of a spindle motor 435.
In such structure, the voltage Va is applied across the metal at the tip end of the optical fiber 433 (probe 436) and the surface of the recording medium 434. Consequently, the electrostatic attractive force is exerted therebetween. The electrostatic attractive force is proportional to the square (value) of the voltage Va and inversely proportional to the square value of the distance d between the probe 436 and the recording medium 434. On the other hand, the force between the atoms, that is, the shear force is the exponential function of the distance d between the probe 436 and the surface of the recording medium 434 and decreases exponentially.
Consequently, since the attenuation of the electrostatic attractive force to the distance d is considerably gentle (slow) compared with that of the shear force, even though the distance d between the probe 436 and the surface of the recording medium 434, the approach therebetween can be grasped as the decrease in the amplitude of the crystallized quartz vibrator 443. The distance d depends on the value of the voltage Va. However, when the value is several tens V (voltage), even though the distance between the probe 436 and the surface of the recording medium 434 is almost several tens um, the amplitude decrease of the crystallized quartz vibrator 443 can be grasped. The extent of the possibility of grasping the approach between the probe 436 and the surface of the recording medium 434 from the distance therebetween can be adjusted by the voltage Va. When the approach therebetween from the further distant place is intended the grasp, the voltage Va should be made further large.
At the time of waiting, the slider 454 is brought, on the recording medium 434, into contact therewith. At this time, although the spindle motor 435 is rotated or stopped, it is more preferable to stop the spindle motor 435 in consideration of the risk of the occurrence of the contact between the probe 436 and the surface of the recording paper.
Before performing the operations of writing-in and reading-out, on the condition that the voltage Va is applied across the probe 436 and the recording medium 434, the crystallized quartz vibrator 443 and the probe 436 is vibrated with the resonance frequency, the vibration amplitude of the probe 436 is always monitored from the output signal of the crystallized quartz vibrator 443, the voltage of rapid ramp rate is applied to the piling-layer type piezoelectric element 445, and the probe 436 is caused to approach the surface of the recording medium 434. When the amplitude of the vibration becomes small, the voltage of the piling-layer type piezoelectric element 445 is held, and thereby the operation of causing the probe 436 to approach the surface of the recording medium 434 is stopped.
Furthermore, the electric potential difference between the probe 436 and the recording medium 434 is eliminated, and then the voltage of slow ramp rate is applied to the piling-layer type piezoelectric element 445. Thereby, the tip end of the probe 436 is caused to approach the surface of the recording medium 434 with low speed by use of a slightly-moving actuator (piezoelectric, etc.) such that the distance between the tip end of the probe 436 and the surface of the recording medium 434 becomes a desired value (distance). Thereafter, the operations of writing-in and reading-out are stated.
As an example, at the time of waiting, since the tip end of the probe 436 and the surface of the sliding-proof pad 446 are brought into contact with the surface of the recording medium 434, the height of the contact surface therebetween becomes same as that of the surface of the recording medium. In such structure, the slider 454 is made previously so as to obtain almost 0.5 um.
Furthermore, for instance, the voltage Va is set to almost 2V. The vibration amplitude of the probe 36 is always monitored from the output signal of the crystallized quartz vibrator 443. The voltage of the rapid ramp rate is applied to the piling-layer type piezoelectric element 445, and then the probe 436 is caused to approach the surface of the recording medium 434.,
When the distance between the probe 436 and the surface of the recording medium 434 becomes almost 2.00 nm, the vibration amplitude of the crystallized quartz vibrator 443 is reduced by the action of the electrostatic attractive force between the probe 436 and the surface of the recording medium 434. The computer 441 grasps the reduction of the vibration amplitude and holds the voltage of the piling-layer type piezoelectric element 445, and further stops the approach of the probe 436 onto the surface of the recording medium 434.
If the approach of the probe 436 onto the surface of the recording medium 434 is detected and stopped from the distance of almost 200 nm, there occurs no collision of the probe 436 onto the surface of the recording medium 434 owing to the over-run from the detection to the stopping. Consequently, the first approach can be done at a comparatively low speed (approx. 0.1 um/s).
Furthermore, the switch 455 is next changed over to the GND (ground) side. Thereby, the electric potential difference disappears between the probe 436 and the surface of the recording medium, and thereby the electrostatic allractive force is not exerted upon both of them. Thereafter, the voltage of the slow ramp rate is applied to the piling-layer type piezoelectric element 445, and the tip end of the probe 436 is caused to approach the surface of the recording medium 434 with low speed (approx. 10 nm/s). When the probe 436 approaches the surface of the recording medium 434 to the extent of several tens nm, the vibration amplitude of the crystallized quartz is reduced due to the shear force between the probe 436 and the surface of the recording medium 434. When both of them approach each other to a desired distance, the computer 441 grasps it and stops the displacement (deviation) of the piling-layer type piezoelectric element 445.
At this time, since the speed of the approach becomes slower than that of the previous stage (step), the over-run becomes small. Consequently, even through the distance between the probe 436 and the surface of the recording medium becomes small, there is no fear that both of them collide against each other. Thereafter, the operations of writing-in and reading-out are started.
As mentioned heretofore, when the distance between the probe 436 and the surface of the recording medium 434 is large, both of them are caused to approach each other with high speed, and at the same time the approach between both of them is grasped from the stage of long distance therebetween and thereby the collision with each other can be prevented. By stepwisely reducing (both of) the electric potential difference and the approaching speed between the probe 436 and the surface of the recording medium 434, the aforementioned sequence can be done. In the last (final) approach, the applying of the voltage across both of them is eliminated and the distance detection therebetween is performed by the action of the shear force, and then the approach is finished.
When the detection of the distance therebetween is done only by the action of the shear force, since the approach of each other therebetween cannot be detected until both of them approach each other to several tens nm, it is necessary to perform the approach of the both with very slow speed of several tens nm/s from the beginning of the approach. Therefore, very long time is consumed till the time of starting the writing-in and reading-out operations. However, according to the method of the background art 12, since it is possible to select the approaching speed corresponding to the distance between the probe 436 and the surface of the recording medium 434, the time needed until the time of starting the operation of writing-in and reading-out can be shortened.
Heretofore, the background art regarding the optical information recording and reproducing apparatus has been described. However, according to such background art which is disclosed in the background-art document, e.g., the specifications of Japanese Laid-open Patent Publication Nos. 7-192280, 8-321084, 8-7323, 9-17047, 7-225975, 7-21564, 10-172172, and other documents, etc., there exists no advantageous functional effect for improving the optical information recording and reproducing apparatus. The present invention has been made in view of the above-mentioned problems and other problems in order to solve such unfavorable problems.
Accordingly, to state concretely in more detail, the present invention solves the background-art defects as mentioned heretofore in the preceding articles, background arts 1 through 12. The present invention provides the optical information recording and reproducing apparatus solving the above matters. The invention provides the optical information recording and reproducing apparatus capable of realizing fine actuation of the extent of several nm in order to perform the correction of tracking with simple structure.
Generally, the probe is movably controlled for tracking. The probe has to be actuated so as to surely move it in the direction perpendicular to the direction of arranging the data row on the recording medium. The aforementioned background arts 1 and 2 do not describe at all any actuation medium. The present invention provide the optical information recording and reproducing apparatus capable of satisfying the demand of moving the probe in such direction.
Furthermore, when the structure of actuating the probe by the action of the electrostatic attractive force, the force is inversely proportional to the square of the distance between the probe and the electrode, and the force of pulling back the probe to the initial position by the spring is proportional to the distance therebetween. Consequently, when the probe goes once out of the stable area (the area where the distance between the probe and the electrode becomes equal to or less than ⅔ of the initial value, the electrostatic attractive force exceeds the force of the spring and thereby the probe is attracted to the electrode. As the result, the operation inevitably becomes very unstable.
The present invention can provide the optical information recording and reproducing apparatus capable of improving such unstable operation and widening the actuatable area, that is, the tracking movable area of the probe.
Since the probe has structure of the cantilever on which the base portion is fixed, the moving distance of the tip end thereof becomes large. When the tracking area needs to be widened, the distance between the electrode and the tip end of the probe is enlarged. However, when the probe is actuated by the electrostatic force, if the distance between the electrode and the probe is long, there arises a defect that, although the movable distance is long, large voltage has to be applied in order to move the probe.
On the other hand, if the distance therebetween is short, there arises another defect that, although even small voltage can actuate the probe, the movable distance inevitably becomes small.
The present invention can provide the optical information recording and reproducing apparatus capable of improving the above-mentioned problems and realizing the large tracking movable distance with low voltage.
Furthermore, both of the voltage applying circuit for applying the voltage between the electrode and the probe and the measurement circuit for measuring the distance therebetween have to operate with high speed and low noise. The present invention can provide the optical information recording and reproducing apparatus capable of satisfying such demand as mentioned above.
In the background art 3, it is necessary to prepare the light source, the lens, and the optoelectric conversion element, etc. only for obtaining the tracking error signal, in addition to the probe for performing the operations of writing in and reading out by use of the evanescent light, for the purpose of obtaining the tracking error signal.
In the background art 4, it is necessary to prepare the adjacent field probe only for obtaining the tracking signal.
In the background art 5, the probe has to be devised so as to emit the ellipse flat spot light, and in addition the wobble pit is formed on the recording medium in order to obtain the tracking error signal. For this reason, there arises a troublesome matter the density of recording the information is lowered.
In the background art 6, it is necessary to prepare the light source, the lens, and the optoelectric conversion element, etc. only for obtaining the tracking error signal, in addition to the probe for performing the operations of writing in and reading out Furthermore, only in order to obtain the tracking error signal, the land needs to be formed on the optical information recording medium. Thereby, there arises a troublesome matter that the density of recording the information is lowered.
The present invention can provide the optical information recording and reproducing apparatus capable of obtaining the tracking error signal with the simplified medium.
Furthermore, in the background art 7, the distance between the tip end of the probe and the surface of the recording medium is measured by the value of the electrostatic capacitance between the conductive part at the tip end part of the probe and the surface of the recording medium. Consequently, there arises a problem that the surface of the recording medium needs to be conductive and there are many restrictions in the structure of the recording medium. However, although the conductive ferromagnetic substance (body) is employed as the material of the recording medium, such substance cannot be applied to the media using the phase variation material requiring the non-conductive protection film. Furthermore, there arises a troublesome matter that the measurement circuit for, measuring the electrostatic capacitance needs to be prepared, and the square measure of the metal film at the tip end of the probe has to be made equal to or more than 500 nmxc3x97500 nm in order to obtain the sufficient measurement accuracy, and therefore, the restriction at the side of the probe turns out to be large inevitably.
In the background art 8, it is necessary to prepare another light source of different wavelength for measuring the distance between the measuring the distance between the tip end of the probe and the surface of the recording medium in addition to the light source for performing the operations of recording and reproducing.
In the, background art 9, there arises a troublesome matter that a pattern of different spatial frequency needs to be prepared on the recording medium in order to measure the distance between the tip end of the probe and the surface of the recording medium and thereby the density of recording on the recording medium becomes lowered inevitably. Furthermore, there arise another troublesome matter that the operation of analyzing the frequency of the obtained signal needs to be done, and much time is needed for those processes, and as the result, the distance between the tip end of the recording medium cannot be controlled with sufficiently high speed.
The present invention can provide the optical information recording and reproducing apparatus capable of solving all of the above-mentioned troublesome matters.
The present invention can provide the optical information recording and reproducing apparatus capable of capturing (knowing) the distance between the tip end of the probe and the surface of the recording medium with the simple medium. The present invention can provide the optical information recording and reproducing apparatus capable of measuring the distance therebetween with high accuracy. The present invention can provide the optical information recording and reproducing apparatus capable of performing the operations of writing in and reading out with high speed by use of the small-sized recording/reproducing head.
The present invention further can provide the information recording and reproducing apparatus capable of solving the problems of the background arts 10 through 12. In particular, for solving the background art 11, the voltages V1 and V2 to be applied to the electrodes 422 and 423 are the voltages obtained by superposing the bias voltage Vb on the control voltage xcex94V for moving the probe 411 in the tracking direction as shown in the equations (5) and, (6). On this occasion, since the control voltage xcex94V or the bias voltage Vb is put in the floating state, there arises a problem of difficulty in the circuit construction such as the stability of the electric potential.
The present invention can provide the information recording and reproducing apparatus capable of improving the stability of the control voltage for tracking the probe and, in addition, simplifying the circuit construction.
Furthermore, according to the background art 11, as the method of applying the voltage to the electrodes 422 and 423, there are disclosed, in the above background art, the method of applying the voltage only to the electrode 422 or 423 in the direction of desiring (intending) to move the probe 411 and the other method of to superposedly applying the bias voltage Vb and the control voltage xcex94V to both of the same electrodes. The latter method may be better than the former method.
However, the matter demanded as the apparatus is not only the controlling property but the possibility of driving the probe with as lower voltage as possible. In particular, regarding the control voltage required the response property in the high frequency, the low voltage can more easily realize the high-speed circuit than the high voltage.
In such situation as mentioned above, the present invention can provide the information recording and reproducing apparatus capable of specifying the condition of surely not only improving the control property but lowering the control voltage and reducing the burden of the circuit (cost, power consumption, size, etc.).
Furthermore, according to the background art 12, the DC voltage Va is applied to the probe 436 in order to attain a rapid approach to the recording medium 434. On the other hand, in the background art 11, the bias voltage Vb is applied between the electrodes 422 and 423 for tracking the probe 411 and the probe itself 411, for the purpose of lowering the control voltage xcex94V and realizing the linearity between the voltage and the movement of the probe 411. For this reason, if the DC voltage Va is applied to the probe 436 in order to attain the rapid approach as in the case of the background art 12, the condition of apply the voltage thereto goes out of the adequate bias condition.
Furthermore, in the background art 10, the patterns 402 and 403 of the different spatial frequency have to be provided on the recording medium 401 in order to measure the distance between the tip end of the probe 404 and the surface of the recording medium 401, and as the result, the density of recording turns out to be low inevitably. Furthermore, the frequency of the obtained signal has to be analyzed. Thereby, much time is required for performing such processes and therefore the distance cannot be controlled with sufficiently high speed.
In such situation as mentioned above, the present invention can provide the information recording and reproducing apparatus capable of realizing, at the same time, the improvement of the control property and the reduction of the control voltage, the small probability of impingement of the tip end of the probe upon the recording medium, and the high operational speed of the approach. Furthermore, the invention can provide the information recording and reproducing apparatus not requiring any of the specified wavelength, the pattern formed on the recording medium, and the signal processings taking much time.